Is there any way to "revive" them by applying higher charge voltage or
something?

"Chris F." wrote in message
...
I got a couple of rather large gel-cell batteries the other day (the
largest is a 12V 24ah) but it turns out they weren't such a great find.
Neither will take a charge; with the charger connected, neither battery
will
draw so much as a single milliamp. Both batteries have a number of little
round covers; underneath the covers are small rubber caps covering a hole.
I
noted that when I removed one of the rubber caps, there was a small inrush
of air as if there was a vacuum inside. My guess is that both batteries
have
"dried up", possibly from lack of use. Is it as simple as adding water,
and
if so, exactly how much and what kind (distilled, tap, etc) should be
used?
Thanks for any advice.